1. Technical Field of the Invention
The invention relates to a method for detecting the presence of liquid in a compressor used to circulate a fluid which may be present in the liquid state or the gaseous state.
2. Description of the Background Art
Under certain circumstances droplets of liquid may be present at the suction inlet of a compressor such as a compressor used in particular to circulate a refrigerating fluid in a circuit of an air conditioning device for the passenger compartment of an automobile vehicle. The said droplets cause a malfunctioning of the compressor and also premature wear of the components of the circuit and decrease the thermal efficiency.
Such an effect may be detected in particular in a circuit such as those described in FR-A-2 717 126 and FR-A-2 731 952, comprising a first branch containing an evaporator followed by the said compressor, a second branch containing a condenser and a third branch not containing a condenser, the second and third branches being positioned parallel to one another so as to form, a cooling loop and a heating loop with the first branch, respectively, switching means being provided to send the fluid emerging from the first branch either into the second branch or into the third branch, and the device also comprising means to send into the passenger compartment air which has been subjected to a heat exchange with the evaporator.
When the fluid circulates in the heating loop, the evaporator is used as a heat exchanger for heating the passenger compartment. In the said loop the fluid normally remains in the gaseous state, but liquid droplets may form by condensation in the evaporator, in particular at low temperatures.
The object of the invention is to detect the presence of liquid at the suction inlet of the compressor without calling upon special sensors which would add greatly to the cost of the circuit.
The invention is based on the discovery that the said presence of liquid causes oscillations in the delivery pressure of the compressor, and these oscillations may be distinguished by their amplitude and their frequency from variations due to other causes.